I'm still dabbling in the use of pgfplots but I'm trying to draw arrows on this plot to show an inverse correlation between the variation in the arc length along the curve and the changes in x.
Given that a picture is worth a thousand words, I'll show you my code, the corresponding output and an image of the desired output, so that you can compare and notice the changes I'd like to get.
Also, you might notice my code is based on the information I collected from these posts: Draw Arrows outside of content-area of TikZ, Tikzpicture - Arrow next to/under plot label and Pgfplots: plot text along function. However, I just haven't been able to make it work together.
I've been struggling with this all night long, so sny help is highly appreciated. In fact, if you could add some explanations on how and why your solution works, so that I can learn from it and do better in the future I'd be forever in debt with you :')
This is my code:
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{decorations.markings,decorations.text,arrows.meta,arrows}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{figure}[htb]
\centering
\begin{tikzpicture}
\begin{axis}[
name=MyAxis,
xlabel={$x$},
ylabel={$y$},
xmin=0,
xmax=25,
ymin=0,
ymax=21,
axis y line=center,
axis x line=center,
ytick=\empty,
xtick=\empty,
]
\addplot[black,domain=0:21,samples=200,very thick]{(-5/4)*21^(3/5)*x^(2/5)+5*x^(8/5)/(16*21^(3/5))+315/16};
\addplot[draw=none,
postaction={decorate,decoration={text effects along path,
text={Increasing values of s},raise=2ex,
text align=center,
text effects/.cd,
text along path,
every character/.style={fill=white,text=blue, yshift=-0.5ex}
}},
domain=0:21,
] {(-5/4)*21^(3/5)*x^(2/5)+5*x^(8/5)/(16*21^(3/5))+350/16};
\addplot+[mark=none,blue,
domain=2:15,latex-,samples=150
] {-(5/4)*21^(3/5)*(x-1.5)^(2/5)+5*(x-1.5)^(8/5)/(16*21^(3/5))+(350/16)};
\end{axis}
\def\myShift{-1cm}
\draw [-latex] ([yshift=-4ex]MyAxis.outer south west) --node[midway, fill=white, yshift=1pt]{Increasing values of $x$} ([yshift=-4ex]MyAxis.outer south east);
\end{tikzpicture}
\caption{Path travelled by dog after $t$ seconds}
\label{ref:my7graph}
\end{figure}
\end{document}
This is the output I get:
This is what I'd like to get:
Notice the changes:
- Shorter horizontal arrow below the x axis.
- Zero at the origin.
- White background for the text along the curved arrow.
- If possible, I'd like to type the "s" in mathmode along the curved arrow.
Edit
These days I read part of the TikZ manual, as well as this and this manual, and found a rudimentary solution. Hopefully someone might come up with a better idea.
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{decorations.markings,decorations.text,arrows.meta,arrows}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{figure}[htb]
\centering
\begin{tikzpicture}
\begin{axis}[
name=MyAxis,
xlabel={$x$},
ylabel={$y$},
xmin=0,
xmax=25,
ymin=0,
ymax=21,
axis y line=center,
axis x line=center,
ytick=\empty,
xtick=\empty,
legend entries={$y(x)$},
legend pos=north east]
\addlegendimage{no marks,dashed,very thick,gray}
]
\addplot[gray,dashed,domain=0:21,samples=200,very thick]{(-5/4)*21^(3/5)*x^(2/5)+5*x^(8/5)/(16*21^(3/5))+315/16};
\addplot[draw=none,
postaction={decorate,decoration={text effects along path,
text={Increasing values of s},raise=-0.5ex,
text align=center,
text effects/.cd,
text along path,
every character/.style={text=blue}
}},
domain=0:17.5,
] {(-5/4)*21^(3/5)* (x-1.31684)^(2/5)+(5*(x-1.31684)^(8/5))/(16*21^(3/5))+(315/16)+1.15223};
\addplot[stealth-,blue,very thick,samples=200,domain=2:3]{(-5/4)*21^(3/5)* (x-1.31684)^(2/5)+(5*(x-1.31684)^(8/5))/(16*21^(3/5))+(315/16)+1.15223};
\addplot[blue,very thick,samples=200,domain=11.75:14]{(-5/4)*21^(3/5)* (x-1.31684)^(2/5)+(5*(x-1.31684)^(8/5))/(16*21^(3/5))+(315/16)+1.15223};
\end{axis}
\draw (0,0) node [below left] {$0$};
\draw [anchor=base, very thick] (4ex,-3ex)--(10ex,-3ex) node [right] {Increasing values of $x$} [-stealth, xshift=28ex](6ex,-3ex)--(12ex,-3ex);
\end{tikzpicture}
\caption{Inverse correlation between $s$ and $x$}
\label{ref:fig2}
\end{figure}
This is the output:
As you might see, I found a way to add a label for the origin and shorten the arrows, but haven't been able to type the blue 's' in mathmode. Again, any help is highly appreciated :)
